Factors influencing the dissolution of phosphate rock in a range of high P-fixing soils from Cameroon

A laboratory incubation experiment was conducted to evaluate the soil factors that influence the dissolution of two phosphate rocks (PRs) of different reactivity (Gafsa, GPR, reactive PR; and Togo-Hahotoe, HPR, low reactivity PR) in seven agricultural soils from Cameroon having variable phosphorus (P)- sorption capacities, organic carbon (C) contents, and exchangeable acidities. Ground PR was mixed with the soils at a rate of 500 mg P kg 21 soil and incubated at 30 degrees C for 85 days. Dissolution of the PRs was determined at various intervals using the Delta NaOH-P method ( the difference of the amount of P extracted by 0.5 M NaOH between the PR-treated soils and the control). Between 4 and 27% of HPR and 33 and 50% of GPR were dissolved in the soils. Calcium (Ca) saturation of cation exchange sites and proton supply strongly affected PR dissolution in these soils. Acid soils with pH-(H2O), < 5 (NKL, ODJ, NSM, MTF) dissolved more phosphate rock than those with pH-(H2O) > 5 (DSC, FGT, BAF). However, the lack of a sufficient Ca sink in the former constrained the dissolution of both PRs. The dissolution of GPR in the slightly acidic soils was limited by increase in Ca saturation and that of HPR was constrained by limited supply in protons. Generally, the dissolution of GPR was higher than that of HPR for each soil. The kinetics of dissolution of PR in the soils was best described by the power function equation P At B. More efficient use of PR in these soils can be achieved by raising the soil cation exchange capacity, thereby increasing the Ca sink size. This could be done by amending such soils with organic materials.

Think local, act local? Issues of co-ordination and integration in Local Agenda 21

The political response to the complex package of environmental problems which threaten the future of our planet has been to introduce a new agenda of environmental action based on the principles of sustainability and subsidiarity. This has been crystallised in world agreements signed at the Earth Summit in Rio. One of these, Agenda 21, calls for the governments and communities of the world to prepare action plans for their areas which can build consensus between the various stakeholder groups and feed the principles of sustainable development back into their policies and day-to-day practices. This paper explores the experience of Local Agenda 21 type processes at three levels in the South East of England: the regional, county (sub-regional) and local level. In particular it undertakes a critical appraisal of the success of these participatory and consensus-building exercises in developing an integrated and co-ordinated approach to environmental action planning. It concludes that, although much useful work has been done in raising awareness and modifying policy and practice, there are significant cultural and institutional barriers which are hindering progress.